It is known to provide a so-called head-up display in, for example, an automobile so as to be able to present certain images to the driver or passengers while they are looking through the windshield.
The present invention is directed to head-up display apparatus that presents images for this, or other applications, volumetrically, meaning that the image appears to exist within a volume in the three-dimensional real world, even though it does not. A volumetric display achieves that appearance by presenting light rays to the observer that are substantially indistinguishable from light rays that would reach the observer from a real object in the real world. Such a volumetric display can imbue the overhead navigation cable with such depth cues such as stereoscopic disparity, motion parallax, convergence and focus.
A particular embodiment of our head-up display includes a projection screen, light projector apparatus configured to project one or more images onto the projection screen, viewing optics through which a viewer can view the projection screen, and a computer, wherein the projection screen is moveable under control of the computer in such a way as to adjust positions of the projection screen and to thereby adjust the distance between the projection screen and the viewing optics during at least a portion each of a succession of refresh periods. As a result, portions of an image projected on the projection screen appear to the viewer to be at particular respective different depths within a three-dimensional image based on the respective positions of the projection screen at the time that those portions are projected on the projection screen.